As disclosed in copending applications Ser. No. 242,493 (Niebylski), filed Sep. 9, 1988 now U.S. Pat. No. 5,045,399; Ser. No. 261,104 (Niebylski) and Ser. No. 261,612 (Niebylski), both filed Oct. 24, 1988; and Ser. No. 272, 258 (Niebylski) now abandoned and Ser. No. 272,481 (Niebylski) now U.S. Pat. No. 4921, both filed Nov. 17, 1988, and Ser. No. 301,450, filed Jan. 25, 1989, now abandoned, normally oxidizable materials such as carbon/carbon composites can be protected from oxidative deterioration at elevated temperatures by the provision of ceramic coatings derived from polysilazne or organoborosilazane polymer compositions which may have ceramic or preceramic powders dispersed therein.
Copending application Ser. No. 301,449 (Niebylski), filed Jan. 25, 1989, now abandoned teaches that outstanding protection from oxidative deterioration at elevated temperatures can be obtained by the use of ceramic coatings having at least one layer derived from a polysilazane-containing composition and at least one layer derived from an organoborosilazane polymer-containing composition. However, it has been found that a disadvantage of at least some of these multi-layer coatings is that cracking is apt to occur when ceramic layers derived from polysilazine-containing compositions are applied over ceramic layers derived from organoborosilazane polymer-containing compositions.